CN107431059B

CN107431059B - Archimedes spiral design for deformable electronics

Info

Publication number: CN107431059B
Application number: CN201580077410.9A
Authority: CN
Inventors: 姜汉卿; 吕程; 于宏宇
Original assignee: Arizona Board of Regents of ASU
Current assignee: Arizona Board of Regents of ASU
Priority date: 2015-01-02
Filing date: 2015-12-30
Publication date: 2020-03-17
Anticipated expiration: 2035-12-30
Also published as: US10660200B2; WO2016109652A1; US20170290151A1; CN107431059A

Abstract

The invention provides an electronic device, which comprises a first functional body, a second functional body and at least one connecting component for connecting the first functional body to the second functional body. The at least one connecting member has a spiral pattern and is suspended in air to allow for extension, bending or compression.

Description

Archimedes spiral design for deformable electronics

Cross Reference to Related Applications

This application claims priority from U.S. provisional patent application No.62/099,324 filed on day 1, 2, 2015, the entire disclosure of which is incorporated herein by reference.

Technical Field

The present application relates to deformable electronic devices, and more particularly to a serpentine electrical interconnect for use in an island interconnect deformable electronic device.

Background

In recent years, rapid development of deformable electronic devices has emerged, which is an attractive and promising new technology. Such electronic devices may be incorporated into wearable devices, such as flexible displays, stretchable circuits, hemispherical electronic eyes, and epidermal devices, among others. With the deforming electronics, the device can be manufactured to fit a variety of physical spaces without the standard geometric constraints of non-deforming electronics. In fact, such devices can be developed for various applications on a nanometer, micrometer, centimeter or meter scale.

Many methods have been used to form deformable electronic devices, and there are generally two conventional approaches. The first approach is to use inherently stretchable organic materials to form electronic devices; however, these organic materials are not suitable for high performance electronic devices because of their low electrical mobility (i.e., the ability of charged particles to pass through a medium in response to an electric field). A second approach utilizes an "island interconnect" structure in which a plurality of inorganic electronic devices are each disposed on a rigid island (e.g., substrate) and electrically connected by a stretchable interconnect, thereby making the entire island interconnect system stretchable. Island interconnect structures are typically supported by elastomeric substrates, and recent developments in foldable electronic devices utilize the concept of paper folding (i.e., paper folding) to increase the flexibility and deformability of the resulting structure. Indeed, one of the main aims is to increase the flexibility and deformability of the extensible electronic devices to allow them to be used in a wider variety of applications than previously possible. With the island interconnect approach, known interconnects are patterned to form serpentine shapes or semi-similar serpentine shapes to improve deformability. The serpentine-based design utilizes kirigarni (i.e., guillotine) concept to create non-straight lines from two-dimensional planes such that in-plane stretching is compensated by out-of-plane distortion. However, even serpentine-based designs are limited in their stretch properties.

Therefore, additional methods of forming interconnects that improve scalability are needed so that electronic devices with a wide range of functionality and modified portability can be developed.

Disclosure of Invention

To improve the deformability of the island interconnect structure, the present invention relates to a spiral-based interconnect that is more stretchable than conventional serpentine-based interconnects.

Accordingly, one aspect of the present invention relates to an electronic device including a first functional body, a second functional body, and at least one connecting member connecting the first functional body to the second functional body, wherein the at least one connecting member has a spiral pattern and is suspended in air to allow expansion, bending, or compression.

Drawings

These and other features of the preferred embodiments of the present invention will become more apparent in the detailed description, which proceeds with reference to the accompanying drawings, wherein:

1(A) -1(C) are top views of three interconnect structure geometries according to embodiments of the present invention;

FIGS. 2(A) - (C) are top views of the three interconnect geometries shown in FIGS. 1(A) - (C) illustrating exemplary dimensions of each according to embodiments of the present invention;

FIGS. 3(A) - (C) are top views of three interconnect structures shown in FIGS. 1(A) -1(C) in deformed and undeformed states;

fig. 4(a) - (C) are graphs depicting the strain behavior of each of the three interconnect structures shown in fig. 2(a) - (C);

FIG. 5 is a top view of a spiral interconnect structure according to an embodiment of the present invention;

FIG. 6(A) is a top view of a modified spiral interconnect structure according to an embodiment of the present invention;

FIG. 6(B) is a graph depicting the strain behavior of the modified spiral interconnect structure of FIG. 6 (A); and

fig. 7(a) - (B) are top views of island interconnect structures formed by the spiral interconnect of fig. 1(C) according to embodiments of the invention.

Detailed Description

The present invention relates generally to a spiral-based interconnect geometry for island-interconnected deformable electronic devices. A deformable electronic device typically comprises a plurality of individual electronic devices electrically connected by one or more connecting members (also referred to as interconnects). The connecting member is electrically conductive so as to allow electrical signals to be conducted between the individual devices. The electronic device is not particularly limited, and may be, for example, energy storage and energy devices (e.g., batteries, solar cells, and supercapacitors), consumer products (e.g., foldable displays, lighting devices, antennas, and foldable toys), and wearable electronic devices (e.g., health monitoring systems and communication systems). The interconnect geometry of the present invention allows these products to be made more compact, portable, and durable without sacrificing performance.

As described herein, and without being bound by any particular theory, it is believed that the spiral-shaped interconnect allows for increased stretchability of the island interconnect device. It is believed that the uniform and small curvature in the spiral pattern for the interconnects contributes to greater stretchability. Instead of applying periodic patterns to the design of interconnects, non-periodic patterns provide a higher degree of freedom during the design process, especially under certain extreme conditions.

As described herein, the spiral interconnect geometry has a higher stretchability than known serpentine-based interconnect geometries. The spiral interconnections can stretch up to 250% under elastic deformation and up to 325% without failure.

Exemplary in-plane shapes of three interconnection patterns (also referred to as "connecting members") are shown in fig. 1(a) - (C), as follows: a conventional serpentine (fig. 1(a)), a self-similar serpentine (fig. 1(B)), and an archimedean spiral structure 100 (fig. 1 (C)). Conventional serpentines (fig. 1(a)) have been widely used to form interconnects and are known in the art, and self-similar serpentines patterns have recently been investigated (fig. 1 (B)). The archimedean spiral structure 100 shown in fig. 1(C) is the primary object of the present invention.

The interconnects of fig. 1(a) - (C) may be formed from materials configured to withstand applied bending stresses formed when adjacent and neighboring functional bodies move relative to each other, thereby forming a resulting electronic device. In one embodiment, the interconnect may include at least one flexible layer (not shown). For example, the interconnects may be formed from a relatively soft material, such as a polymer, gel, or the like. The polymer may be, for example, Parylene (poly-para-xylylene) or a conductive polymer (Parylene-C), polyimide, Polydimethylsiloxane (PDMS). Alternatively, the interconnects may be formed of any conductive material known in the art to be suitable for use as a conductor, such as metals (e.g., copper, chromium, aluminum, gold, silver, iron, cobalt, titanium, etc.), nanofibers, conductive oxides (e.g., ZnO, Indium Tin Oxide (ITO), fluorine doped tin oxide (FTO), ReO)₃、IrO₂、CrO₂Etc.) and positive temperature coefficient thermistors (PTC) and negative temperature coefficient thermistors (NTC).

In another example, the interconnect may be formed from multiple layers, such as a first layer forming the top or bottom of the interconnect or a dual layer and/or multiple layers on both the top and bottom of the interconnect as desired depending on the requirements of a particular application.

Each of the geometries shown in fig. 1(a) - (C) may have any dimensions suitable for the particular application and known to those skilled in the art. In one exemplary embodiment shown in fig. 2(a) - (C), each pattern is formed from an interconnect 102 having a thickness (not shown) of about 1 micron and an interconnect width (w) of about 40 microns. The radius (r) of the conventional serpentine of FIG. 2(A) and the semi-similar serpentine of FIG. 2(B) are about 20 μm and 10 μm, respectively. The length (l) of each serpentine fold of a conventional snake is about 310 microns, and the length (l) of each serpentine fold of a self-similar snake₁，l₂) 235 microns and 580 microns respectively. These dimensions are provided by way of example only, and any dimensions suitable for a particular use or application may be used.

In one exemplary embodiment, the archimedean spiral structure 100 may be specified by an analytical function in polar coordinates as r ═ a · θ^qWhere r is the radius of the spiral pattern and θ is [0,3 π ═]A is the geometric pre-factor and q is the power that determines the shape of the function. The values of the variables a or q are not limiting, they are related, and determine the shape of the spiral pattern. In another exemplary embodiment, the archimedean spiral structure 100 is defined by an analytical function in polar coordinates as r ± 60 θ^1/1.7，θ＝[0,3π]Where r is the radius of the spiral pattern. In one embodiment, the body width (w) of the spiral structure 100 is about 40 microns. In this way, all three patterns (fig. 2(a) - (C)) have approximately the same span of about 1000 μm in the x-direction, the same height of about 400 μm in the y-direction, and the same profile length of about 5.650 μm. In one embodiment where copper is used to form the interconnect, the Young's modulus E is 119GPa and the Poisson's ratio v is 0.34. Plasticity is considered and described as

Wherein epsilon_YYield strain, E, when equal to 0.3%_p530MPa and n 0.44.

To compare the interconnect geometries of fig. 2(a) - (C), a uniform standard was developed. For a typical island interconnect structure, in an unconstrained state, the islands, also referred to as functional bodies, should occupy a large portion of the in-plane area to increase area coverage. By way of example, 2mm x 2mm islands and 1mm gaps between islands may be used, where the 2mm x 2mm island size is consistent with the size of some small conventional electronic chips and the area coverage may reach over 45%. Thus, the area filled by the interconnects (i.e. the connecting members) is 2mm x 1 mm. In this region, one interconnect or a plurality of interconnects may be used. The use of a plurality of interconnects is preferred in view of the conductivity of the resulting structure, since a break in one interconnect does not lead to an electrical failure of the entire structure. Thus, in one embodiment, four identical interconnects are placed in the gaps between each island, and each interconnect occupies no more than 0.5mm (height) by 1mm (width) of space. Another criterion for uniformly comparing the stretchability among the different interconnects shown in fig. 1(a) - (C) is that the same cross-sectional area and in-plane profile length of each island should be used, so that the resistance among the different interconnects remains consistent.

To analyze the extensibility of each of the interconnect geometries shown in fig. 2(a) -2(C), finite element analysis was performed using the commercially available finite element analysis software ABAQUS (manufactured by Dassault systems of Velizy-Villacoublay, france). Buckling analysis was performed to obtain the first ten buckling modes, then with random weight factor input as a defect. During analysis, a 20-node quadratic (C3D20R) with reduced order integrals is used and mesh convergence is ensured. Next, a prescribed displacement force is applied to the rightmost end of each interconnection to stretch the interconnection while the leftmost end remains fixed. At certain loading steps, the prescribed displacement force is removed to determine if the deformation is recoverable.

The results of the extensibility test are shown in fig. 3(a) - (C). These figures show the elastic extensibility of each of the three patterns of fig. 2(a) - (c) under the same in-plane span and contour length constraints. Elastic extensibility is defined herein as the critical strain interconnected into the region of plastic deformation, i.e., where the maximum equivalent strain exceeds the yield strain. The recovery after removal of the stretching force was also analyzed. Thus, for each three interconnect geometry, both the deformation state at critical strain and the release state when the stretching force is removed are shown, with the legend showing the equivalent plastic strain. For comparison, two states of interconnection (deformed and relaxed) at the mid-point of critical strain are also provided, still within the elastic range, so that the deformation is fully recoverable.

As shown in fig. 3(a) -3 (C), the results clearly show that the archimedean spiral structure 100 has the greatest elastic stretchability, up to 200%, whereas the conventional serpentine and self-similar serpentine have elastic stretchability of 112% and 98%, respectively. The illustration of the deformed state shows that for each interconnect, in-plane stretching is accompanied by out-of-plane deformation (mainly twisting and bending). In other words, out-of-plane distortion compensates for in-plane distortion. Especially for the archimedean spiral structure 100, splay-like deformation occurs to compensate for in-plane stretching. From an application point of view, a low level of out-of-plane deformation is required in order to allow the devices to be stacked more densely in the thickness direction. When the critical strain is released, the interconnect returns almost to its undeformed shape, even when plastic deformation has occurred. This is because at or slightly above the critical point, the area into the plastic region is very limited and most interconnects remain within the elastic domain. The plastic deformation is located at the area with large curvature.

The strain behavior of each interconnect pattern tested above is provided in the graphs of fig. 4(a) - (C). Here, the stretchability of each interconnection is defined as the critical strain at which the maximum value of the maximum principal strain exceeds the breaking strain by 1%. Fig. 4(a) - (C) also show out-of-plane distortions among these three interconnect patterns. The legend indicates the percentage of material with plastic deformation. Here, it is shown that the archimedean spiral structure 100 still has an extensibility up to 270%, while the other two serpentine structures have a lesser extensibility of about 220%. The archimedean spiral structure 100 has the highest level of out-of-plane distortion because the outer loop of the spiral is rotated to compensate for in-plane stretching, but the maximum out-of-plane distortion, 300 μm, is within the thickness of the island or device, which does not affect the stacking density in the vertical direction. As shown in the legend, the percentage of plastic deformation is quite small, about 1%, which indicates that the helical structure 100 has a good ability to return to its undeformed state even after entering the plastic deformation zone.

A comparison of the illustrations in fig. 3(a) - (C) and fig. 4(a) - (C) shows that uniform and small curvatures of the interconnect pattern may contribute to greater stretchability with the same in-plane span and contour length constraints. The regular and semi-similar serpentine shapes (fig. 1(a) and 1(B), respectively) have zero curvature on their straight line segments, but have a large curvature at the junction between their straight lines. Due to design constraints based on serpentine structures, a large curvature is required to have a large face fill ratio. Thus, the curvature based on the serpentine varies from zero curvature to large curvature along its length, which results in lower stretchability.

According to another embodiment, as shown in fig. 5, a modified spiral structure 102 is used to form the interconnection, wherein the curvature develops smoothly along the length of the profile, making it elongated. In one embodiment, the modified spiral structure has a polar angle ranging from 0 to 3 π.

In another embodiment, two archimedean spiral structures 100 are used to form the interconnect. To make the spiral-based structure more versatile so that it can better fit into non-square areas, a modified archimedean spiral structure 100' can be used, as shown in fig. 6 (a). Here, the ratio between the horizontal and vertical dimensions is adjusted to fit in the non-square area. This approach modifies the original archimedean spiral structure 100 by multiplying a smooth approximation by a step function of theta in a polar coordinate system, and then inserting straight lines to fit in-plane regions. As shown in fig. 6(a), the interconnect width (w) is 40 microns and the length (l) of each fold is 300 microns, but any particular size suitable for use in a particular application may be used.

The stretchability of the modified archimedean spiral structure 100' is analyzed by applying a prescribed displacement force at one end while securing the other end, as described herein. The results of this extensibility test are provided in fig. 6 (B). The results of the original spiral structure 100 are plotted on fig. 6(B), using the same legends as used in fig. 4(a) - (C). It is evident that the graph shows that the modified archimedean spiral structure 100' is more stretchable than the original spiral structure 100, with an elastic stretch of more than 250% and a stretch of 325% before breaking. The maximum out-of-plane displacement is about 450 μm, which is an acceptable level. Without being bound by any particular theory, it is believed that the modified archimedean spiral structure 100' is more stretchable because the newly added straight portions 104 allow the structure to more easily produce out-of-plane deformations without introducing large curvatures.

In one aspect, the spiral structure 100 is coupled to and positioned between opposing functional bodies 700 to form an island interconnect structure 702, as shown in fig. 7 (a). In another embodiment shown in fig. 7(B), two spiral structures 100 are used to form an island interconnect structure 702'. In an alternative embodiment, the island interconnect structure 702 may be formed from a plurality of spiral structures 100, each spiral structure 100 being coupled to an opposing functional body 700. Thus, each interconnection is selectively movable between a fixed position, at which relative movement between the connected functionalities 700 is not allowed, and a bendable (pliable) position, at which relative movement between the connected functionalities 700 is allowed.

Although several embodiments of the present invention have been disclosed in the foregoing specification, it should be understood by those skilled in the art that many modifications and other embodiments of the invention are contemplated which have the advantages of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Furthermore, although specific terms are employed herein, as well as in the claims that follow, they are used in a generic and descriptive sense only and not for purposes of limiting the described invention, nor the claims that follow.

Claims

1. An electronic device, comprising:

a first functional body;

a second functional body; and

at least one connecting member connecting the first functional body to the second functional body, wherein the at least one connecting member has a spiral pattern and is suspended in air to allow for expansion, bending, or compression,

wherein the spiral pattern is an archimedean spiral.

2. The electronic device of claim 1, wherein the archimedean spiral is defined by a function r ═ a · θ^qProvision is made wherein r is the radius of the spiral pattern and θ ═ 0,3 π]A is the geometric pre-factor and q is the power that determines the shape of the function.

3. The electronic device of claim 1, wherein the archimedean spiral is defined by a function r ═ 60 θ^1/1.7Provision is made wherein r is the radius of the spiral pattern and θ ═ 0,3 π]。

4. The electronic device of claim 1, wherein the archimedean spiral is elongated.

5. The electronic device of claim 1, wherein the at least one connecting member is selectively movable between a fixed position and a bendable position such that the first functional body is movable relative to the second functional body, and vice versa.

6. The electronic device of claim 1, wherein the at least one connection member is a conductor.

7. The electronic device of claim 6, wherein the at least one connection member is made of copper, chromium, aluminum, gold, silver, iron, cobalt, titanium, conductive nanofibers, ZnO, Indium Tin Oxide (ITO), fluorine doped tin oxide (FTO), ReO₃、IrO₂、CrO₂Poly-p-xylene,parylene-C, polyimide or polydimethylsiloxane.

8. The electronic device of claim 1, wherein the at least one connection member has a thickness of about 1 micron.

9. The electronic device of claim 1, wherein the electronic device is a battery.

10. The electronic device of claim 1, wherein the at least one connecting member has an elastic stretchability of up to 200%.

11. The electronic device of claim 1, wherein the at least one connection member comprises at least two electrically connected connection members, each connection member having a spiral pattern.

12. The electronic device of claim 11, wherein the at least two electrically connected connecting members have an elastic stretchability of up to 250%.

13. The electronic device of claim 1, wherein the electronic device comprises a plurality of functional bodies, each functional body being connected by at least one connecting member having a spiral pattern.

14. The electronic device of claim 1, wherein the at least one connecting member is formed of multiple layers.

15. The electronic device of claim 14, wherein at least one of the multiple layers is a flexible layer.